This invention relates to a method of preparing aromatic oligomers such as arylene ketone oligomers and arylene sulfone oligomers, and in particular to an electrophilic reaction process for preparing such oligomers in the presence of a Lewis acid and a complex between a Lewis acid component and a Lewis base component and, optionally, a diluent.
Arylene ketone and arylene sulfone oligomers can be prepared by either one of two approaches: (1) electrophilic synthesis in which an aryl ketone or aryl sulfone linkage is formed or (2) nucleophilic synthesis in which an aryl ether linkage is formed. In an electrophilic synthesis, the reaction involves the formation of an aryl ketone group or aryl sulfone group from a carboxylic acid derivative or sulfonic acid derivative, respectively, and an aromatic compound containing an aromatic carbon bearing an activated hydrogen atom, i.e. a hydrogen atom displaceable under the electrophilic reaction conditions. The monomer system employed in the reaction can be, for example, (a) a single aromatic compound containing a carboxylic acid derivative or sulfonic acid derivative as well as an aromatic carbon bearing a hydrogen atom activated toward electrophilic substitution; or (b) a two-monomer system of a dicarboxylic acid derivative or a disulfonic acid derivative and an aromatic compound containing two such activated hydrogen atoms. An example of a single monomer system is p-phenoxybenzoyl chloride. An appropriate two-monomer system comprises 1,4-diphenoxybenzene and terephthaloyl chloride. Combinations of several such monomers can be used.
Electrophilic reactions of this type are often referred to as Friedel-Crafts reaction. A commonly used medium for such Friedel-Crafts reactions consists of the reactant(s), a catalyst, such as anhydrous aluminum trichloride, and an inert solvent such as methylene chloride. Because carbonyl groups complex with aluminum trichloride and thereby deactivate it, the aluminum trichloride catalyst is generally employed in the preparation of arylene ketones in an amount slightly more than one equivalent for each equivalent of carbonyl groups in the reaction medium. The slight excess assures that enough free aluminum chloride will be present to fulfill its catalytic role. In the preparation of arylene sulfones similar amounts of aluminum trichloride are required for each sulfone group under the preferred reaction conditions. Other metal halides such as ferric chloride may be employed as the catalyst.